hey everybody...first, thank you so much for your help, especially
Weasel and
DW2 . i think i MAY have figured things out... we won't know for sure for sure of course, bc no control group (sad trombone sound) but i might have some kind of explanation.
after DW commented about the keep in dark space instructions on the bottle, i decided to do some testing of possible causes... so i put the ph down bottle itself in a dark , cool, dry cabinet. before it had been in a bathroom cabinet (so dark, but not necessarily cool and def not dry)
then i threw away all pipettes, plastic containers, anything that had come in physical contact w/the rancid water got trashed or boiled. so that way, the next time i "worked with" ph downed H20 i would have controlled for prior contamination.
having done that,then, the next time i was making up my baby batch o' germination water, i put the mixed water itself into a lightproof container with an open top. so the only exposure to light that the "new" ph-downed water had was the circumference of the top of the cup itself... since doing that, i have not had the smell once. so i THINK that MAYBE that light warning on the label maybe extends to the mixed water itself, even though General Hydroponics does not say so on the bottle...
otherwise i truly have no explanation....but if ^^^ is the explanation at least now i know and maybe this thread will help some future person who has a similar problem.
thank you again, weasel and dw2...